Physiology of everyday sleep and physical activity: An exploratory mixed-methods study of multi-sensor wearables for infants and toddlers.

Sleep and physical activity are vital to the health, development, and well-being of young children. To effectively promote these behaviours at the population level, better tools for objectively quantifying them are needed. This hypothesis-generating mixed-methods study explored the potential usability of two wearable sensors to measure physical activity and sleep in young children over multiple days, drawing on physiological measurements. A longitudinal within-case design was employed, in which families with children aged 4-36 months from the North East of England were recruited through playgroups and social networks. Parents and children tested two wearable devices in a structured play setting and at home over a period of 1 week. Data on sleep, movement, and heart rate were collected using the Bittium Faros 180 heart rate monitor and the NAPPA sleep monitoring system. Usability was assessed through researcher observations and parent feedback using ethnographic methods. Wear time, heart rate variability during naps, and ultradian respiration cycles during sleep were analysed. Seven children participated and completed the study. While parents were initially enthusiastic, usability challenges arose. The heart rate monitor was considered uncomfortable, its large size hindered activity, and electrodes were detached by parents and accidently, leading to significant data loss. The NAPPA was easier to use, discreet, and comfortable, but disrupted sleep routines. Additional challenges related to non-parental caregiving resulted in non-wear and/or data loss. These results indicate that wearable devices for young children hold potential but face significant design challenges for longitudinal home use at scale. Co-creation of child-friendly, practical hardware and software is essential for effective, large-scale health monitoring in young children.